The popularity of minimally invasive surgery has been growing rapidly due to its association with decreased complication rates and post-surgical recovery times. The instruments employed are generally hand-operable and typically include a handle, a shaft that may or may not be rotatably attached to the handle, a rotation knob rigidly fixed to the proximal end of the shaft near the handle in instances where the shaft is rotatably attached to the handle, and a tool or end effector attached to the distal end of the shaft. To manipulate the instruments, they are held at the handle and typically pivoted about a pivot point defined by the entry incision, i.e., the incision made in the abdominal wall for laparoscopic procedures. The end effector may also be rotated about the shaft axis, as for example, by rotating a rotation knob, if present. In use, these instruments have limited control and range of motion and become physically taxing as the length of the procedure increases.
Surgical procedures such as endoscopy and laparoscopy typically employ instruments that are steered within or towards a target organ or tissue from a position outside the body. Examples of endoscopic procedures include sigmoidoscopy, colonoscopy, esophagogastroduo-denoscopy, and bronchoscopy, as well as newer procedures in natural orifice transluminal endoscopic surgery (“NOTES”). Traditionally, the insertion tube of an endoscope is advanced by pushing it forward, and retracted by pulling it back. The tip of the tube may be directed by twisting and general up/down and left/right movements. Oftentimes, this limited range of motion makes it difficult to negotiate acute angles (e.g., in the rectosigmoid colon), creating patient discomfort and increasing the risk of trauma to surrounding tissues.
Laparoscopy involves the placement of trocar ports according to anatomical landmarks. The number of ports usually varies with the intended procedure and number of instruments required to obtain satisfactory tissue mobilization and exposure of the operative field. Although there are many benefits of laparoscopic surgery, e.g., less postoperative pain, early mobilization, and decreased adhesion formation, it is often difficult to achieve optimal retraction of organs and maneuverability of conventional instruments through laparoscopic ports. In some cases, these deficiencies may lead to increased operative time or imprecise placement of components such as staples and sutures.
Recently, surgical instruments, including minimally invasive surgical instruments, have been developed that are more ergonomic and which have a wider range of motion and more precise control of movement. These instruments may include mechanisms that articulate using a series of links coupled with one or more sets of tension bearing members, such as cable. As with conventional instruments used in minimally invasive surgery, rotation of the shaft and end effector with respect to the handle is an important feature of cable and link type instruments to aid with dissecting, suturing, retracting, knot tying, etc. Ergonomic, flexible, and intuitive mechanisms that facilitate manual control of the end effectors of such instruments are also important factors as medical procedures become more advanced, and as surgeons become more sophisticated in operating abilities. Particularly with regard to rotation, however, inadvertent rotation and larger torques can be associated with articulating instruments, as loading on the end effector that can be off axis from the shaft axis. Consequently, new mechanisms and methods for controlling rotation of surgical instruments are desirable.